1. Field of the Invention
The present invention relates to a method and an apparatus for discrimination between optical discs of different types, which discriminates between optical discs of a plurality of types having different record densities of recorded information.
2. Description of Related Art
Making the recording density of an optical disc higher relates to shortening the wavelength of the read-out light irradiated on the optical disc for reading recorded information. That is, the wavelength of the read-out light for an optical disc having a higher recording density is shorter than the wavelength of the read-out light for an optical disc having a lower recording density. This means that an optical disc has a wavelength of read-out light suitable for its recording density. Therefore, it is sometimes impossible to read recorded information using read-out light of a shorter wavelength from an optical disc having a recording density corresponding to read-out light of a relatively longer wavelength. For example, in the case of a CD-R, it has a reflectivity of nearly 80% for read-out light of a wavelength of about 780 nm, but has a reflectivity of nearly 10% for read-out light of a wavelength equal to or less than 750 nm. Thus, a wavelength of about 780 nm is desirable in order to obtain read-out signals (RF signals) having good spatial-frequency characteristics. On the other hand, in the case of DVD having a high recording density, read-out signals having sufficient spatial-frequency characteristics cannot be obtained and the recorded information cannot be reproduced without using read-out light of a wavelength of about 650nm.
Incidentally, it is more advantageous for the user, compared with using individual players, from the point of view of installation space and price, that a plurality of optical discs having suitable read-out light of different wavelengths such as CD-R and DVD can be reproduced with the same optical disc player.
However, a general-purpose optical disc player for reproducing optical discs of a plurality of types needs to comprise a plurality of light sources for emitting read-out light of wavelengths different from each other and needs to select a light source rapidly, from the plurality of light sources, corresponding to the type of the optical disc that has been set, so that the type of optical disc that has been set needs to be discriminated immediately and correctly.
An object of the present invention is to provide a method and an apparatus for discrimination between optical discs of different types, which can discriminate immediately and correctly the types of a plurality of optical discs having different record densities of recorded information from each other.
The optical disc discrimination method according to the present invention is an optical disc discrimination method for discriminating between at least two types of optical discs having recording densities of recorded information, different from each other; characterized in that an optical disc to be discriminated is driven to rotate, a read-out light beam is irradiated on the optical disc to be discriminated by performing at least a focus servo operation as a servo operation, an RF (Radio Frequency) signal is obtained by receiving a reflected light beam from the optical disc to be discriminated, the RF signal is converted into binary digits as a pulse train signal, the number of pulses in the pulse train signal is counted for a predetermined time, a count value during the predetermined time is compared with a threshold value, and the optical disc to be discriminated is determined to be one of the at least two types of optical discs, having the least amount of recording density, when the count value within the predetermined time is equal to or less than the threshold value.
Furthermore, the optical disc discrimination apparatus according to the present invention is an optical disc discrimination apparatus for discriminating between at least two types of optical discs having record densities of recorded information, different from each other; characterized by having a means for driving the optical disc to be discriminated to rotate, a read-out means for performing at a least focus servo operation as a servo operation to irradiate a read-out light beam on the optical disc to be discriminated and for receiving a reflected light beam from the optical disc to be discriminated to obtain an RF signal, a converting means for converting the RF signal into binary digits as a pulse train signal, a counting means for counting the number of pulses in the pulse train signal for a predetermined time, a comparing means for comparing a count value during the predetermined time with a threshold value, and a determination means for determining the optical disc to be discriminated to be one of at least two types of optical discs, having the least amount of recording density, when the count value within the predetermined time is equal to or less than the threshold value.